Dishwasher having improved heating means

ABSTRACT

A dishwasher having an improved arrangement for heating the washing compartment. A sheath-type electric heating element disposed in the bottom of the compartment is enclosed by a tubelike shield of greater diameter than the heating element. The shield prevents direct radiation from the electric-heating element to the walls of the compartment, and itself acts as a secondary heating surface of greater area and lower temperature than the heating element for effectively heating the interior of the compartment.

United States Patent lnventors Thomas E. Jenkins;

Donald S. Cushing, Louisville, Ky. 815,033

Apr. 10, 1969 Jan. 12, 1971 General Electric Company a corporation of New York Appl. No. Filed Patented Assignee DISHWASHER HAVING IMPROVED HEATING MEANS 7 Claims, 5 Drawing Figs.

US. Cl 219/335,

134/108: 219/316 Int. Cl F24h l/00 Field of Search 219/310.

[56] References Cited UNITED STATES PATENTS 2,838,642 6/1958 Araldsen 219/534 3,049,136 8/1962 Van Scoyk 134/108X 3,446,939 5/1969 Morgan et al 219/316 Primary Examiner-.l. V. Truhe Assistant ExaminerC. L. Albritton Attorneys-James E. Espe, Harry E. Manbeck, Jr., Joseph B.

Forman, Oscar B. Waddel] and Frank L. Neuhauser ABSTRACT: A dishwasher having an improved arrangement for heating the washing compartment. A sheath-type electric heating element disposed in the bottom of the compartment is enclosed by a tubelike shield of greater diameter than the heating element. The shield prevents direct radiation from the electric-heating element to the walls of the compartment, and

itself acts as a secondary heating surface of greater area and lower temperature than the heating element for effectively heating the interior of the compartment.

: J NMIQW N 3t55SL2-42 INVENTORS i THOMAS E. ramams & DONALD s. cusHmG Y WZWL THEN? ATTORNEY DISHWASHER HAVING IMPROVED HEATING MEANS BACKGROUND OF THE INVENTION Domestic dishwashers are commonly provided with heating means for heating th water during the washing cycle and for drying the dishes after the washing cycle is completed. Sheathtype electric resistance heating elements disposed in the bottom of the washing compartment have been extensively used for this service. The sheathed-heating units are desirable since they will withstand the severe operating conditions encountered during the washing cycle but yet are relatively inexpensive and simple to mount in the machine.

Certain problems are, however, created by the sheathed electric-heating elements due to the high surface temperatures which they obtain. For example, it is common for the heater surface, i.e., the exterior of the sheath, to reach temperatures in the range of l200 F. to l400 F. during operation. This high temperature may result in overheated areas of the dishwasher walls and the dishes due to radiation effects, the radiation effects varying by the fourth power of the absolute sheath temperature. Also, it may cause ignition of objects such' as plastic spoons, wooden handles, cloth, etc., which inadvertently come into contact with the heating element. A further problem inherent with sheathed heating elements is a somewhat poor heat transfer to the air within the dishwasher compartment during the drying cycle because of the relatively limited surface area of the heating elements.

Accordingly it is an object of our invention to provide a new and improved heating arrangement for dishwashers which will retain the advantages of the electric sheath-type heating units but will obviate the above noted problems.

A further object is to provide an improved heating arrangement for dishwashers, which is particularly effective to heat the air within the dishwasher compartment and thereby to dry the dishes themselves.

SUMMARY OF THE INVENTION By our invention we provide a dishwashing machine having an improved heating means mounted in the washing compartment. The heating means comprises a sheath-type electricalheating element and a tube-like shield which is combined with it. The shield has a greater diameter than the heating element and is mounted around it so that an air space is formed between them. With this arrangement direct radiation is prevented from the heating element to the walls of the dishwasher compartment, while the shield itself is heated to a temperature lower than that of the heating element. The exterior surface of the shield being exposed to the washing compartment acts as a secondary heating surface of greater area and lower temperature for effectively heating the interior of the compartment. The larger area of heating surface provides improved heat transfer to convecting air within the compartment, with hot spots on the compartment wall or the dishes being avoided due to the lower temperature of the shield.

By a further aspect of our invention the shield is mounted around the electric-heating element in such a manner that only limited heat conduction occurs between the two, thereby avoiding hot spots on the shield. Also, the shield and the mounting are so constructed and arranged as to provide for irregular heater shapes, such as U-shaped arrangements, which are desirable for dishwasher applications.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a front elevational view, partially broken away and partially in section, of a household dishwasher incorporating our new and improved heating means in one preferred form thereof.

FIG. 2 is a plan view showing the bottom wall of the washing compartment of the dishwasher with the improved heating means mounted thereon.

FIG; 3 is a cross-sectional view taken on the line 3-3 of FIG. 2, showing the heating means and the center-mounting bracket.

FIG. 4 is a cross-sectional view taken on the line 4-4 of FIG. 2, showing the arrangement at one end of the heating means and FIG. 5 is a perspective view of a spacer element incorporated in the heating means.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 of the drawing we have shown therein an automatic household dishwasher l which incorporates an improved heating arrangement embodying our invention in one preferred form thereof. The dishwasher includes a cabinet or housing 2 within which is defined a dishwashing chamber or compartment 3. Access to the washing compartment 3 is obtained by means of a door 4 which pivots about an axis adjacent its bottom edge so as to open the front of the washing compartment. When the door 4 is pivoted to a horizontal position, upper and lower racks 5 and 6 may be pulled partially out of the washing compartment so as to load and unload the dishwasher with dishes. It will be understood that suitable sealing means are provided between the door 4 and the front edge of the cabinet 2 so as to prevent escape of water from the washing compartment 3 during the operation of the dishwasher.

The supply of wash water to the washing compartment is controlled by means of a solenoid valve 7 positioned in the inlet water line 8 to the machine. When the valve 7 is opened, water is introduced into the wash compartment 3 through an opening 9 in the back wall of the washing compartment. It will be understood that a suitable cover or outer wall is provided behind the opening 9 so as to prevent loss of water from compartment 3 during the operation of the dishwasher.

The opening and closing of the inlet valve 7 is controlled by means of a sequence timer 10 mounted on the door 4. The timer 10 also serves to control all of the other electrical com ponents of the dishwasher and causes it to progress automatically through a complete dishwashing cycle including a rinsing operation, a washing operation and a drying operation.

During the rinsing and washing operations the water introduced into the wash chamber is circulated throughout the chamber so as to wash dishes carried by the racks 5 and 6. The circulation is accomplished by means of a spray arm 11 which is rotatably mounted above the bottom wall 12 of the washing compartment. The spray arm 11 is supplied with water by a pump 13 which is driven by an electric motor 14. The pump 13 withdraws the wash water from the washing compartment 3 through a sump 15 which opens through the bottom wall 12 of the compartment. The sump, as shown in FIG. 1, is connected to the pump 13 by means of a flexible conduit 16, a bafl'le 17 (FIG. 2) at the entrance serving to limit noise during the pump operation. The water drawn into the pump through the conv duit I6 is discharged by the pump during the washing'and rinsing operation through a conduit 18 which connects to the rotatable spray arm 11. The spray arm discharges the water upwardly in a series of jets which issue from the spray' arm through the plurality of orifices 19 provided in its upper surface. At least some of the orifices 19 include exit surfaces inclined from the vertical so that a reaction effect is created as the water passes through them. This reaction effect causes the spray arm to rotate and thereby the jets of water discharged by it effectively project into all areas of the dishwashing compartment to provide effective cleaning of the dishes.

Following the washing and rinsing operations, the water is exhausted from the wash compartment 3 through a suitable drain line 19a. The pump 13 acts as a drain pump for that purpose, a suitable solenoid valve in the pump housing being operated by the timer 10 during the drain operations so as to close the recirculation conduit 18 and open the drain line 19a.

In accordance with our invention an improved heating at" rangement is provided in the washing compartment 3 for heating the wash water during the rinsing and washing operations and for drying the dishes during the drying operation, which follows the washing operation. The heating arrangement includes a sheath-type electric resistance heating element 20 and a shield 21 which is positioned around the heating element. As best shown by FIGS. 1 and 2 this heating means is mounted between the bottom wall 12 of the washing compartment and the lower su. ace of the spray arm 1 1. In particular, the heating means is supported by the bottom wall at its outer ends, the terminal sections of the electric-heating element 20 turning downwardly and passing through the wall at points 22 and 23 to provide that support. A third point of support is provided by a bracket 24 which is attached to the bottom wall 12 by suitable means such as a bolt 25. The bracket 24 carries the shield 21 adjacent its center and includes a hook or tab 26 at its upper end which grips the shield to prevent any lateral movement of it.

It will be understood that the sections of the heating element 20 which pass through the bottom wall 12 are so called cold end terminals. In other words, the center resistance wire or coil 27 of the heating element 20 (FIG. 3) does not extend to the outer ends of the heating element but rather terminates at each end somewhat short of the depending sections of the heating element. Lead-in wires 28 pass upwardly through the depending sections of heating element 20 to connect to the ends of the heater coil 27 and no heating is provided in the lead wire sections. It will be noted that the heating element 20 comprises a more or less conventional sheathtype electric resistance unit in which the space 29 between the heating coil 27 and the outer sheath 30 is filled with a suitable granular, electrically insulative, heat conducting material such as magnesium oxide.

The outer shield 21, which is preferably formed of stainless steel surrounds the entire heating section of the heating element 20. As is shown in FIGS. 3 and 4, the shield 21 comprises a tubelike element of substantially greater diameter than the heating element 20 and it is closed at its opposite ends by suitable end caps 31 and 32. The above-mentioned cold end terminals of the heating element 20 extend inwardly past the end caps 30 and 31 so that the shield 21 thus surrounds the entire heated portion of heating element 20. It will be noted that the shield 21 is formed of two parts 33 and 34 which both extend from one end cap to the other. In the preferred embodiment shown each of these parts is curved or arcuate in cross section and they are crimped together at 35 and 36 to provide a unitary shield structure. Crimping has proved to be an inexpensive but effective way of attaching the shield parts together but this will be understood that other suitable means could be used if so desired.

The shield 21 is positioned around the heating element 20 by a plurality of suitable spacers. These spacers comprise the end caps 31 and 32 and a plurality of clip elements 37. As is best seen in FIGS. 3 and the clip elements 37 include a central U-shaped section including oppositely disposed concave sections which fit tightly over the outer sheath 30 of the heating element 20. The clips then engage the shield 21 on one side of the heating element at their bight sections 38 and on the other side by means of arcuate sections 39 extending outwardly from the legs of the U. With this arrangement the clips or spacers 37 keep the shield 21 securely mounted on the heating element 20 with an appropriate air space 40 being maintained between the heating element and the shield. As before-mentioned, the end caps 31 and 32 also act as mounts or spacers for the shield 20. As shown in FIG. 4 each of these end caps includes a central opening 41 which fits over the heating element, and they extend outwardly from this central opening so as to fit over and around the ends of the shield 21. With this arrangement they effectively position the ends of the shield 21, thereby maintaining the same space between the shield and the heating element 20 at the ends as is provided by the clips 37 in the middle sections of the shields.

The spacers in the illustrated embodiment, i.e., the clips 37 and the end caps 31 and 32, are preferably formed of the same material as the shield 21 itself; namely, stainless steel. With the spacers being formed of thesame' material, electrolytic deterioration is avoided between the spacers and the shield. Also there is only limited heat conduction from the heating element 20 through the spacers. Stainless steel being a poor heat conductor and the spacers being very thin in cross section, the heat conduction through them is not large and thereby hot spots on the shield are avoided.

In our preferred embodiment the sheathed heating element 20 has an outside diameter of about 0.270 inches and it has an output of about 20 to 25 watts per linear inch. With a heater of this physical size and electrical output we prefer to use an outer shield 21 of about 1% inch diameter. Thus the shield is of considerably greater diameter and surface area than the sheath 30 of the heating unit 20 and there is a space of approximately 0.5 inches between the heating element 20 and the shield 21 at all points along the heating section of the heating element. In our preferred embodiment the stainless steel shield is about 0.010 inch in thickness. The spacers, i.e., the end caps 31 and 32 and the clips 37, may also be formed about the same thickness of stainless steel. It is preferred that the center-mounting bracket 24 be formed of the same material, and as shown in FIG. 3 it is channel shaped except at the end tab or hook 26.

With this heater construction there is no direct radiation from the sheathed-heating element 20 to the walls of the washing compartment 3 or to dishes positioned in the racks 5 and 6. Instead all direct radiation is blocked by the shield 21. Thus during the operation of the heating element, whether in the washing and rinsing operations or in the drying operation the shield 21 is heated whenever the heating element 20 is energized. In particular the shield may be heated to approximately 500 F. to 600 F. when the surface temperature of the heating element 20 is at 1200 F. to 1400F. The shield heated to this temperature in turn passes heat to the dishwasher compartment. It is not hot enough to cause overheating of the dishwasher walls or of the dishes by radiation, but on the other hand it does provide effective heating of the water during the washing cycle and the rinsing cycle and of the dishes themselves during the drying cycle. In fact, it has been found that improved heat transfer to the convecting air is provided during the drying cycle. The outer face of the shield 21 acts as a heating surface of a much greater area than the area of the heater sheath 30 and even though it is at a lower temperature, it is effective to provide good heat transfer to the air and thereby efficient drying of the dishes.

It will be understood that our invention is not limited to a generally circular shield such as that shown. However, it is very desirable that the shield 21 surround the heating element 20 throughout its entire heating section so as to prevent radiation into the dishwashing compartment. It is also desirable that a significant air space be provided between the internal heater and the shield. This air space, together with the larger area of the shield causes it to operate at a lower temperature and thereby provide good heat transfer during the drying cycle without overheating anything in the dishwashing compartment.

1n the manufacture of the dishwasher l the heating means is formed as a subassembly and then is mounted in the dishwash ing compartment 3 as a unit. It will be seen that in the manufacturing process, the spacers, i.e., the clips 37 and the end caps 31 and 32, are first placed on the heating element 20. Then the parts 33 and 34 of the shield 21 are placed over the heating element and are crimped together in proper relation with the spacers. This gives a firm and permanent mounting of the shield around the heating element. With this done the heating element is then placed in the dishwasher and secured in place by means of the bracket 24 and mounting grommets or other suitable means at the points 22 and 23 of the bottom wall 12.

Although, as we have mentioned above, our improved heating means may be used both for heating the water during the washing and rinsing cycle and for drying the dishes, it will be understood that it may, if desired, be used only for water heating or only for drying. It is particularly effective during the drying operation because of the improved heat transfer to the convecting air in the compartment 3.

We claim:

1. ln a dishwashing machine having a washing compartment for accommodating caches to be washed, water inlet and drainage means for said compartment, and means in said compartment to effect water circulation therein; means to heating the interior of said compartment comprising:

a. a sheath type electric heating element mounted in said compartment;

b. a tubelike shield mounted around said heating element;

c. said shield being heated from said heating element and preventing direct radiation from said heating element to the walls of said compartment;

. said shield having a greater diameter than said heating element and being spaced therefrom to form an air space therebetween;

. the exterior surface of said shield being directly exposed to the interior of said compartment whereby said shield acts as a heating surface of greater area and lower temperature than said heating element for effectively heating the interior of said compartment.

2. The invention of claim 1 including a plurality of spacer means of low thermal conductivity mounting said shield around said heating element.

3. The invention of claim 2 wherein said shield and said spacer means are all formed of stainless steel.

4. The invention of claim 2 wherein said spacer means include a pair of end caps mounting said shield on said heating element at the opposite ends of said shield, and at least one internal spacer disposed within said shield, said internal spacer holdingsaid shield in position on said heating element intermediate the ends thereof.

5. The invention of claim 1 wherein said shield includes a plurality of separate parts extending generally the length of said heating element, said separate parts being secured together to form said shield.

6. The invention of claim 1 wherein said heating element and said shield are generally U-shaped from one end to the other, and said shield is supported intermediate its ends by a bracket mounted on the bottom wall of said compartment.

7. The invention of claim 5 wherein said parts forming said shield are generally curved in cross section and wherein said shield and said spacer means are formed of the same material to limit electrolytic deterioration. 

1. In a dishwashing machine having a washing compartment for accommodating dishes to be washed, water inlet and drainage means for said compartment, and means in said compartment to effect water circulation therein; means to heating the interior of said compartment comprising: a. a sheath type electric heating element mounted in said compartment; b. a tubelike shield mounted around said heating element; c. said shield being heated from said heating element and preventing direct radiation from said heating element to the walls of said compartment; d. said shield having a greater diameter than said heating element and being spaced therefrom to form an air space therebetween; e. the exterior surface of said shield being directly exposed to the interior of said compartment whereby said shield acts as a heating surface of greater area and lower temperature than said heating element for effectively heating the interior of said compartment.
 2. The invention of claim 1 including a plurality of spacer means of low thermal conductivity mounting said shield around said heating element.
 3. The invention of claim 2 wherein said shield and said spacer means are all formed of stainless steel.
 4. The invention of claim 2 wherein said spacer means include a pair of end caps mounting said shield on said heating element at the opposite ends of said shield, and at least one internal spacer disposed within said shield, said internal spacer holding said shield in position on said heating element intermediate the ends thereof.
 5. The invention of claim 1 wherein said shield includes a plurality of separate parts extending generally the length of said heating element, said separate parts being secured together to form said shield.
 6. The invention of claim 1 wherein said heating element and said shield are generally U-shaped from one end to the other, and said shield is supported intermediate its ends by a bracket mounted on the bottom wall of said compartment.
 7. The invention of claim 5 wherein said parts forming said shield are generally curved in cross section and wherein said shield and said spacer means are formed of the same material to limit electrolytic deterioration. 